Make head if my figure smoother
This happens due to the n-gon face on top of the head of your figure. They don't subdivide well, so you get some kind of wavy surface.
To avoid this, you should try to keep quads (faces with four vertices) wherever possible.

That means that you shoud put some additional edge loops there, e.g. like that:

What I did was extruding the top face and scaling it down, then repeating the same thing, so that the inevitable transition from quads to one ngon happens in the small area in the middle.

Cheers